This invention relates generally to an electrophotographic printing machine, and more particularly concerns an apparatus for regulating the developability of a development system employed therein.
In the purpose of electrophotographic printing, a charged photoconductive member is exposed to a light image of an original document being reproduced. The irradiated areas of the photoconductive surface are discharged recording thereon an electrostatic latent image corresponding to the informational areas of the original document. A development system moves a developer mix of carrier granules and toner particles into contact with the photoconductive surface. The toner particles are attracted electrostatically from the carrier granules to the latent image forming thereon a toner powder image. Thereafter, the toner powder image is transferred to a sheet of support material. After transferring the toner powder image to the sheet of support material, a fusing device permanently affixes the toner powder image thereto.
It is evident that in a printing machine of this type, toner particles are depleted from the developer mixture. As the concentration of toner particles decreases, the density of the resultant copy degrades. In order to maintain the copies being reproduced at a specified minimum density, it is necessary to regulate the concentration of toner particles in the developer mixture. This is the function of the developability regulating apparatus.
With the advent of multi-color electrophotographic printing, it became highly desirable to mix toner particles of different colors in the developer mixture. In this manner, a mixture of differently colored toner particles produced a new color. For example, equal amounts of yellow and magenta toner particles when mixed together will produce a red color. Similarly, equal amounts of yellow and cyan toner particles will produce green, while equal amounts of magenta and cyan will produce blue. In a system of this type, it is necessary to control the concentration of at least two differently colored toner particles in the developer mixture. It is the function of the developability regulating apparatus to maintain the quantity of differently colored toner particles in the developer mixture at preselected levels so as to achieve the desired resultant color in the mixture. Variations in the quantity of one of the toner particles relative to the other toner particles will produce distortions in the color of the mixture.
Accordingly, it is a primary object of the present invention to improve the developability regulating system for controlling the concentration of a plurality of differently colored toner particles in the developer mixture.